drm: atmel-hlcdc: add missing .set_property helper to the crtc

The default implementation should be used.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1498107791-17450-2-git-send-email-peda@axentia.se